Is there anything better than a buffer?
Sep 05, 2017
Baseline: Conventional till = 1.036 t/y sediment delivery
Absolutely, when it comes to reducing sediment delivery, there are BMPs that definitely outperform buffer strips. Using science developed by USDA’s Agricultural Research Service and Agren®, I looked at the efficacy of buffer strips compared to other practices. Using SoilCalculator®, I modeled the sediment delivery from a 302-acre farm in Western Iowa to a nearby stream. For the baseline conditions, I assumed a corn-soybean rotation farmed with conventional tillage. The resulting sediment delivered to the stream was 1,036 tons/year, with no other BMPs modeled.
By adding a 50-foot wide buffer, the sediment delivery was reduced by 114 tons/year, or a 11% annual decrease. That’s right, only 11%.
82-100% of water enters streams through CFPs
The marginal reduction in soil loss is due to the concentrated flow paths (CFPs) within the field. CFPs have long been identified as a weakness in sediment-reducing buffers. In a study of the Cache River Watershed, in Southern Illinois, Dr. Jon Schoonover found that between 82-100% of the water flowing from fields flowed into streams through CFPs.
Runoff entering field through concentrated flow paths
Again, using my example of the 302-acre field with conventional tillage, I modeled the CFPs through SoilCalculator. Clearly, a large portion of water runoff in this field enters the stream through concentrated flow (shown in red).
When identifying alternatives to a 50-foot buffer that achieve equal or lower sediment delivery, I considered three options; two being tillage options and one option being retention structures.
Changes in tillage provide a significant reduction in both erosion and sediment delivery. Going to just one year of no-till reduces sediment delivery by 41% (or a reduction of 421 tons/year from the baseline). Moving to two years of no-till reduces sediment delivery 10-fold (a reduction of 935 tons/year).
Two basins reduce sediment delivery by 385 t/y.
Another way to achieve a reduction in sediment delivered to the stream is by constructing retention structures, or more specifically, water & sediment control basins. In this 302-acre field, there are multiple potential sites for basins. In the image on the right, I sited 2 different water & sediment control basins. The combination of these 2 basins will reduce the sediment delivery by 385 tons/year, or a 37% reduction. As a bonus, water and sediment control basins reduce rapid runoff thereby changing/improving, the hydrology of the stream.
It is important to consider the cost of each of the three options — a 50-foot buffer, change in tillage practices, and water & sediment control basins. A 50-foot buffer strip on this site would take 12.3 acres of land out of row crops. Assuming the farmer had no use for hay or grazing and the land was valued at $8,500/acre, the buffer could cost upwards of $100,000. (The filter strips could be hayed or grazed but then sediment delivery to the stream would increase.) The planning tools estimated the two water & sediment control basins would cost $25,000, but tile lines used to drain the basins would improve drainage and improve yields. Switching to one or two years of no-till is more difficult to quantify, given such variables as soil types, fertility, weed control and equipment needs. Some farmers say no-till is a break even compared to conventional tillage. Some farmers say no-till reduces yield. Individual farmers, as always, will need to determine the cost/benefit to their unique operation.
If we are going to advance soil and water conservation, we need to stop thinking that one size fits all. Effective conservation planning must analyze the nuances of farmland so we can make the best recommendations to farmers and landowners. The idea of conservation planning has been around for years. Some planning is done on the back of a napkin. Some planning is done with aerial photos and topographic maps. However, the ability of whole farm planning has never been realized, until now, because of lack of science-driven technology. Agren’s sustainability platform allows ag retailers to effectively and efficiently assist farmers with their resource needs and prescribe the all-important precision conservation.
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